Electric vehicles of the type concerned are known from, for example, Japanese Patent Publication No. SHO 48-4260 and Japanese Patent Laid-Open Publication No. 2001-271317.
FIG. 11 hereof diagrammatically shows the electric vehicle as disclosed in the publication No. 2001-271317. The electric vehicle designated generally at 200 is a snow removing machine including a machine body 201. The machine body 201 includes a working apparatus 204 comprised of an auger 202 and a blower 203, an engine 205 for driving the working apparatus 204, left and right traveling apparatuses 206, 206 comprised of crawler belts (not shown), left and right electric motors 207, 207 for driving the traveling apparatuses 206, 206, respectively, a generator 209 driven by the engine 205 to supply electric power to a battery 208 and the electric motors 207, 207, and a control unit 211 for controlling the electric motors 207, 207.
An output from the engine 205 is in part used for driving the generator 209. An electric power generated by the generator 209 is supplied to the battery 208. The left and right electric motors 207, 207 are driven by the electric power supplied from the battery 208 for driving the traveling apparatuses 206, 206. The remainder of the output from the engine 205 is transmitted through an electromagnetic clutch 212 to the working apparatus 204 for driving the working apparatus 204.
Generally, when an electric vehicle of the above type makes a turn rightward or leftward, one of left and right electric motors disposed on the same side as the turning direction of the electric vehicle is decelerated to thereby decelerate a crawler belt disposed on the same side as the turning direction of the electric vehicle. Hereinafter, such an electric motor disposed on the same side as the turning direction of the electric vehicle and a traveling apparatus having the crawler belt disposed on the same side as the turning direction of the electric vehicle refer to “turning-side electric motor” and “turning-side traveling apparatus”, respectively. When the electric vehicle is to be switched in operation from a turning mode to a straight-traveling mode, the turning-side electric motor is gradually accelerated to thereby accelerate the turning-side traveling apparatus gradually.
In case the turning-side traveling apparatus has a very low speed close to zero, however, the speed of the turning-side traveling apparatus is much lower than that of the traveling apparatus disposed opposite the turning-side traveling apparatus. The speed of the turning-side traveling apparatus can not quickly increase and become equal to the speed of the opposite traveling apparatus under such an influence as inertias of the respective traveling apparatuses.
Especially, since the left and right crawler belts of the traveling apparatuses have large surface areas contacting the ground and large driving power, there is a room left for improvement in the electric vehicle to ensure quick and smooth switching of operation of the electric vehicle from the turning mode to the straight-traveling mode.